1. Field of the Invention
This invention is directed to novel olefinic copolymers containing alkylene units, alkylacrylate units and pendant hydrolyzable silane groups. Also, this invention relates to a process for preparing a water curable silane modified alkylene alkylacrylate copolymer. Additionally, this invention relates to an electrical wire or cable insulated with a water-curable silane modified alkylene alkylacrylate copolymer.
2. Description of the Prior Art
It is known to vulcanize polyolefins to extend their service temperature above the melting point of the resin. In areas such as wire and cable, continuous chemical and radiation vulcanization processes are well known. Predominant commercial processes involve a peroxide induced free radical crosslinking reaction. The process steps of coating wire and cable with a peroxide curable coating involve a continuous extrusion of the curable polyolefin composition onto the wire or cable followed by high pressure steam contact (250-300 psi pressure) to initiate peroxide decomposition and rapid vulcanization of the polyolefin composition. When a radiation curable polyolefin coating composition is used to coat a wire or cable, the same procedure is used as that for peroxide curing except that an electron beam is used as the energy source for vulcanization.
However, both the peroxide and radiation curable systems have serious shortcomings, including high capital investment and high energy utilization. Also, when peroxide curing is used, the coating tends to be difficult to carry out since it requires critical control of the process. If the process is carried too far, the polyolefin may crosslink and solidify in the process equipment (scorching). This requires time consuming delays in removing the cross-linked product from the equipment and costly losses of material.
U.S. Pat. No. 3,646,155 issued Feb. 29, 1972, describes a free radical grafting reaction of an unsaturated organosilane onto a polyolefin polymer backbone, i.e., polyethylene or copolymers of ethylene with less than 50 percent of propylene and/or butylene. The resultant thermoplastic material retains normal extrusion processability thereby permitting fabrication or shaping for end-use applications. After the grafting reaction, vulcanization is accomplished by contact with water. Elevated temperatures (80.degree.-100.degree. C.) and a silanol condensation catalyst are used to accelerate the vulcanization.
The reactions may be depicted as follows: ##STR1##
However, the peroxide initiator used in reaction (I) may be reactive toward, and can prematurely cure the polyethylene, i.e., scorch the polyethylene. This results in difficulties in processing for end use applications.